Aircraft Paint Companies Tackle Environmental, Composite Challenges

In the multicolor world of aircraft painting, airlines and independent shops are seeking better performance and optimization, especially with the increasing use of composites and other new materials for airframe applications. For aerospace paint companies, there has been no ebb in pushing the state-of-the-art—beyond what is on the palette.

“In our experience, the switch to base coat-clear coat paint systems and the removal of chrome-containing compounds from primers have been the most significant changes to aircraft paint products over the past few years,” says Emmett Moran, head of operations for Europe, Middle East and Africa at International Aerospace Coatings.

Others agree. The segment’s biggest recent change has been the introduction of base coat-clear coat systems as replacements for high solids topcoats, says Richard Marston, chief commercial officer at MAAS Aviation.

“The base coat-clear coat system saves time on more complex livery applications, with dry to tape times on the colors at around 2-3 hr., as opposed to around 8 hr. for the high solids topcoats,” Marston says. “The clear coat also gives much better UV resistance with color retention and gloss levels lasting much longer. We are now seeing gloss levels remain over 90 gloss units for over eight years.”

Marston adds that the major push by the paint manufacturers in recent years has been to reduce chromates in primers. The newer primers, he explains, are applied in conjunction with water-based pretreatments such as Bogel and Socogel, which he says are easy to apply and, when applied with base coat and clear coat, have increased the life cycle of the coating system.

Developed by Boeing and licensed to outside vendors, Bogel is a pretreatment product applied directly to the bare metal airframe after stripping to promote adhesion to the substrate for the coating system. Socogel, used by Airbus, is a chrome-free product that replaced wash or etch primers containing strontium, a hexavalent chrome, Marston explains.

“The improved hiding power—the amount of paint you have to apply to gain coverage of the substrate—of some base coats has also helped to reduce weight,” Marston says. “And the pretreatments, as part of the new complete system, have improved adhesion on the rivets, helping to vastly reduce rivet rash. Also, the improved UV stability of base coat-clear coat systems has cut the number of paint inputs by extending the life span of the coating.”

Brandon Boyer, paint team leader at Duncan Aviation’s Lincoln, Nebraska, location, reports that paint manufacturers are gaining success with base coats-clear coats, although aircraft size and downtimes can still be issues.

“The idea with base coats-clear coats is more for the appearance of aircraft to relate more closely to the OEM vehicle markets,” Boyer says. “They present more options for brighter, more vibrant colors and products [which are] more easily used for custom painting projects but are still able to hold up to the demanding environments that aircraft go through in a paint life cycle. Also, [they make it] easier to touch up paint areas after they go through maintenance events.”

Rene Lang, executive managing director for aviation at paint manufacturer Mankiewicz, stresses that the development of coatings today is usually demand-driven to optimize and sometimes revolutionize existing solutions.

“We constantly monitor and exchange information on products, materials and processes with our customers on the MRO, airline and aircraft OEM sides,” Lang says. “The focus is often on the robustness of the coating in terms of application conditions.”

Lang says speed is another area of focus, particularly from an optimization perspective. “We not only look at the number of layers and drying times, but also process improvements such as intermediate masking or using one hardener for a full range of products,” he says. “With full orderbooks at OEMs and tight MRO time slots, saving time is essential in coating aircraft.”

Composite Challenges

As Lang also points out, new developments in the aerospace paint industry are often related to the materials used in aircraft construction such as composite components and additive manufacturing, which have emerged in recent years.

“New materials require ideally adapted coating solutions and present new challenges,” Lang says, citing composites as a case in point.

Lang says composites used in structural parts present issues that require high-tech and specially adjusted product solutions because the surfaces are not as smooth as metallic parts. Possible damage spots often caused by the production process of composites are made more apparent by the high-gloss exterior systems, “as if seen through a magnifying glass,” and make the final finish appear uneven and flat, he says. “Those imperfections need to be leveled out before the decorative coats are applied,” he adds.

Lang says Mankiewicz has developed a line of “surface correctors” that can level out nearly all surface defects, reducing the number of scrap parts.

But composite materials present another challenge for the paint companies because they are far more flexible than other substrates. To address that, Mankiewicz has developed Alexit FlexPrimer, which Lang says is “a highly flexible” primer. “Even in areas that are stressed with high levels of vibration—in addition to regular movements in flight, like engine nacelles—the primer provides the required adhesion, maximum flexibility and prevents the coating system from cracking and adhesion loss,” he explains.

Another innovation Lang cites is Alexit WingFlex, which he describes as a “two-in-one” topcoat that can simultaneously be used on upper and lower wing box surfaces. He explains that standard wing coating systems consist of two separate entities—one coat for the upper portion and one for the lower side.

Lang says Alexit WingFlex meets all the environmental challenges to which wings are exposed. For the upper side, high flexibility and UV resistance are required, and the coating needs to withstand the impact of considerable compression caused by movement and the effects of sunlight. On the lower side, wings must resist harsh chemicals like hydraulic fluids. “Also, Alexit WingFlex allows for touch-up and repair, saving time, money and unscheduled maintenance or early refurbishment,” he adds.

Environmental Concerns

Asked about chromate replacements in coatings, Lang cites “sol-gel technology,” which he says can replace primers containing chromates 100%, as well as adhesion promoters and wash primers.

“Replacing chromates in structural part coatings is a vital driver for the Mankiewicz research and development team,” Lang explains. “However, in some areas it is hard to replace chromates due to their strong and unique characteristics which immensely improve durability. The problem is to find a solution that is highly sustainable and offers the same durability and fast-healing properties for corrosion protection as chromates.”

In fact, the removal of chromates and volatile organic compounds (VOC) from aircraft paint has raised durability concerns, as Boyer at Duncan Aviation reports.

“We are hearing concerns expressed by airlines and business aircraft operators that the new paints do not hold up as well as the older systems, as paint manufacturers have developed more sustainable products,” Boyer says.

Expanding Capabilities

AkzoNobel also is expanding its coatings capabilities. One example is the manufacturer’s new ER-100 topcoat, which is specifically engineered to protect critical engine components, Aerospace Segment Manager Celine Dorignac says. Built on the latest polymer technology, Dorignac says ER-100 combines flexibility and hardness, giving essential parts such as leading edges and fan blades robust protection against sand, rain erosion, chemical exposure and UV light.

“While ER-100 isn’t lighter, as a paint, its enhanced erosion resistance means it can achieve the same level of protection with reduced thickness, which helps deliver a savings in weight,” she explains. “Its compatibility with a variety of AkzoNobel primers also ensures versatility on both metal and composite surfaces.”

Dorignac says AkzoNobel is putting its new solar heat-reflective (SHR) paint technology through trials, specifically on its Aerodur 3001 base coat line. The technology is designed to help dark colors absorb less solar heat.

“Our research and development team has been working closely with aircraft manufacturers to create black and dark color options with advanced SHR properties, and which can be applied to composite materials,” Dorignac explains. “They benefit from having a heat-reflective pigment designed to minimize heat build-up and slow material degradation for a just-painted look.”

In addition, Dorignac says AkzoNobel is developing a new generation of waterborne primers specifically designed to adhere to the latest thermoplastic composites, increasingly used in the aerospace industry.

“This new primer represents a significant advancement in application as it adheres effectively without requiring extensive surface treatments, simplifying the preparation process and supporting more efficient application,” Dorignac says. “This not only enhances compatibility with cutting-edge materials but also aligns with the company’s commitment to more sustainable, water-based solutions that reduce the overall environmental impact.”

That primer builds upon AkzoNobel’s efforts to make its latest paint products more sustainable, particularly in the development of chromate-free and VOC-compliant formulations. For instance, Dorignac says AkzoNobel pioneered chrome-free lithium-based exterior primers with the introduction of Aerodur HS 2121 CF and Aerodur HS 2118 CF. Both were designed to provide corrosion protection for aircraft surfaces, enhance system adhesion and increase resistance to hydraulic fluids.

AkzoNobel also recently introduced Aerolith P27-CF, a chromate-free, anti-corrosive polyurethane primer specifically formulated for structural and fuel tank applications. As a three-component system, Aerolith P27-CF provides durable corrosion protection over the life span of an aircraft, Dorignac says. “This new primer leverages similar lithium-based anti-corrosion technology, supporting a more sustainable operation without sacrificing performance,” she adds.

AkzoNobel is also advancing sustainability and durability in composite surfacing, which Dorignac says poses its own set of challenges. “Labor intensive, costly and frequently resulting in surface imperfections that can affect paint adhesion and long-term durability, composite surfaces can also be highly susceptible to UV degradation, further impacting their performance and longevity,” she says.

To mitigate those issues, Dorignac says AkzoNobel is developing a solution that uses a hydroxy-functional, co-curable polyurethane film as an innovative alternative.

“This co-curable film eliminates the need for VOCs in primer application, aligns with environmental goals and supports compliance with increasingly stringent regulations,” she says. “The film also delivers superior UV protection for composite materials, significantly enhancing durability, while providing a smooth, high-quality surface that improves paint adhesion and eliminating the surface preparation steps that cost time and money.”